Clean up code that locates SDK and SDK version.

utils/pub/sdk.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Operations relative to the user's installed Dart SDK.
+library sdk;
+
+import 'dart:io';
+
+import '../../pkg/path/lib/path.dart' as path;
+import 'log.dart' as log;
+import 'version.dart';
+
+/// Gets the path to the root directory of the SDK.
+String get rootDirectory {
+  // If the environment variable was provided, use it. This is mainly used for
+  // the pub tests.
+  var dir = Platform.environment["DART_SDK"];
+  if (dir != null) {
+    log.fine("Using DART_SDK to find SDK at $dir");
+    return dir;
+  }
+
+  var pubDir = path.dirname(new Options().script);
+  dir = path.normalize(path.join(pubDir, "../../"));
+  log.fine("Located SDK at $dir");
+  return dir;

[nweiz, 2013/01/19 00:35:47]

I wonder if we should do some sanity checks here so that we can throw a
reasonable error message if the directory we think contains the SDK actually
doesn't.

[Bob Nystrom, 2013/01/22 23:53:19]

I don't think we've hit issues with this in the wild, at least not yet, so I'm
not too worried here.

+}
+
+/// Gets the SDK's revision number formatted to be a semantic version.
+Version version = _getVersion();
+
+/// Determine the SDK revision number.
+Version _getVersion() {
+  var revisionPath = path.join(rootDirectory, "revision");
+  var revision = new File(revisionPath).readAsStringSync();

[nweiz, 2013/01/19 00:35:47]

Oh synchronous file IO, how lovely you are...

[Bob Nystrom, 2013/01/22 23:53:19]

Oh yeah. I thought about making this async and then remembered that I don't
completely hate myself.

+  return new Version.parse("0.0.0-r.${revision.trim()}");

[nweiz, 2013/01/19 00:35:47]

Another place it would be good to do some validation. We could even print some
instructions on what to do if we've found the SDK but it didn't contain a
revision file.

[Bob Nystrom, 2013/01/22 23:53:19]

Ditto previous comment. I don't mind making this more robust over time but we
haven't seen too many issues here so far.

+}